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Formalize that the Py_VISIT macro requires that the tp_traverse

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implementation it's used in must give its arguments specific names.
This commit is contained in:
Tim Peters 2004-07-15 04:05:59 +00:00
parent 89ba1fff17
commit eda29306b3
3 changed files with 49 additions and 39 deletions
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11
Doc/api/newtypes.tex
View file

@ -1664,13 +1664,14 @@ The \member{tp_traverse} handler must have the following type:
\end{ctypedesc}
To simplify writing \member{tp_traverse} handlers, a
\cfunction{Py_VISIT()} is provided:
\cfunction{Py_VISIT()} macro is provided. In order to use this macro,
the \member{tp_traverse} implementation must name its arguments
exactly \var{visit} and \var{arg}:
\begin{cfuncdesc}{void}{Py_VISIT}{PyObject *o}
Call the \var{visit} for \var{o} with \var{arg}. If \var{visit}
returns a non-zero value, then return it. Using this macro,
\member{tp_traverse} handlers look like:
Call the \var{visit} callback, with arguments \var{o} and \var{arg}.
If \var{visit} returns a non-zero value, then return it. Using this
macro, \member{tp_traverse} handlers look like:
\begin{verbatim}
static int

71
Doc/ext/newtypes.tex
View file

@ -106,7 +106,7 @@ Now if you go and look up the definition of \ctype{PyTypeObject} in
\file{object.h} you'll see that it has many more fields that the
definition above. The remaining fields will be filled with zeros by
the C compiler, and it's common practice to not specify them
explicitly unless you need them.
explicitly unless you need them.
This is so important that we're going to pick the top of it apart still
further:
@ -149,7 +149,7 @@ TypeError: cannot add type "noddy.Noddy" to string
\end{verbatim}
Note that the name is a dotted name that includes both the module name
and the name of the type within the module. The module in this case is
and the name of the type within the module. The module in this case is
\module{noddy} and the type is \class{Noddy}, so we set the type name
to \class{noddy.Noddy}.
@ -180,7 +180,7 @@ This has to do with variable length objects like lists and strings.
Ignore this for now.
Skipping a number of type methods that we don't provide, we set the
class flags to \constant{Py_TPFLAGS_DEFAULT}.
class flags to \constant{Py_TPFLAGS_DEFAULT}.
\begin{verbatim}
Py_TPFLAGS_DEFAULT, /*tp_flags*/
@ -197,8 +197,8 @@ We provide a doc string for the type in \member{tp_doc}.
Now we get into the type methods, the things that make your objects
different from the others. We aren't going to implement any of these
in this version of the module. We'll expand this example later to
have more interesting behavior.
in this version of the module. We'll expand this example later to
have more interesting behavior.
For now, all we want to be able to do is to create new \class{Noddy}
objects. To enable object creation, we have to provide a
@ -268,7 +268,7 @@ Of course, the current Noddy type is pretty uninteresting. It has no
data and doesn't do anything. It can't even be subclassed.
\subsection{Adding data and methods to the Basic example}
Let's expend the basic example to add some data and methods. Let's
also make the type usable as a base class. We'll create
a new module, \module{noddy2} that adds these capabilities:
@ -351,7 +351,7 @@ Noddy_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
Py_DECREF(self);
return NULL;
}
self->last = PyString_FromString("");
if (self->last == NULL)
{
@ -417,10 +417,10 @@ Noddy_init(Noddy *self, PyObject *args, PyObject *kwds)
static char *kwlist[] = {"first", "last", "number", NULL};
if (! PyArg_ParseTupleAndKeywords(args, kwds, "|OOi", kwlist,
&first, &last,
if (! PyArg_ParseTupleAndKeywords(args, kwds, "|OOi", kwlist,
&first, &last,
&self->number))
return -1;
return -1;
if (first) {
tmp = self->first;
@ -488,7 +488,7 @@ this?
garbage collection, there are calls that can be made to ``untrack''
the object from garbage collection, however, these calls are
advanced and not covered here.}
\item
\item
\end{itemize}
@ -527,7 +527,7 @@ sure the members are initialized to non-\NULL{} values, the members can
be set to \NULL{} if the attributes are deleted.
We define a single method, \method{name}, that outputs the objects
name as the concatenation of the first and last names.
name as the concatenation of the first and last names.
\begin{verbatim}
static PyObject *
@ -558,7 +558,7 @@ Noddy_name(Noddy* self)
result = PyString_Format(format, args);
Py_DECREF(args);
return result;
}
\end{verbatim}
@ -656,16 +656,16 @@ Noddy_setfirst(Noddy *self, PyObject *value, void *closure)
PyErr_SetString(PyExc_TypeError, "Cannot delete the first attribute");
return -1;
}
if (! PyString_Check(value)) {
PyErr_SetString(PyExc_TypeError,
PyErr_SetString(PyExc_TypeError,
"The first attribute value must be a string");
return -1;
}
Py_DECREF(self->first);
Py_INCREF(value);
self->first = value;
self->first = value;
return 0;
}
@ -687,11 +687,11 @@ We create an array of \ctype{PyGetSetDef} structures:
\begin{verbatim}
static PyGetSetDef Noddy_getseters[] = {
{"first",
{"first",
(getter)Noddy_getfirst, (setter)Noddy_setfirst,
"first name",
NULL},
{"last",
{"last",
(getter)Noddy_getlast, (setter)Noddy_setlast,
"last name",
NULL},
@ -705,7 +705,7 @@ and register it in the \member{tp_getset} slot:
Noddy_getseters, /* tp_getset */
\end{verbatim}
to register out attribute getters and setters.
to register out attribute getters and setters.
The last item in a \ctype{PyGetSetDef} structure is the closure
mentioned above. In this case, we aren't using the closure, so we just
@ -737,10 +737,10 @@ Noddy_init(Noddy *self, PyObject *args, PyObject *kwds)
static char *kwlist[] = {"first", "last", "number", NULL};
if (! PyArg_ParseTupleAndKeywords(args, kwds, "|SSi", kwlist,
&first, &last,
if (! PyArg_ParseTupleAndKeywords(args, kwds, "|SSi", kwlist,
&first, &last,
&self->number))
return -1;
return -1;
if (first) {
tmp = self->first;
@ -838,11 +838,11 @@ For each subobject that can participate in cycles, we need to call the
\cfunction{visit()} function, which is passed to the traversal method.
The \cfunction{visit()} function takes as arguments the subobject and
the extra argument \var{arg} passed to the traversal method. It
returns an integer value that must be returned if it is non-zero.
returns an integer value that must be returned if it is non-zero.
Python 2.4 and higher provide a \cfunction{Py_VISIT()} that automates
calling visit functions. With \cfunction{Py_VISIT()}, the
Python 2.4 and higher provide a \cfunction{Py_VISIT()} macro that automates
calling visit functions. With \cfunction{Py_VISIT()},
\cfunction{Noddy_traverse()} can be simplified:
@ -856,12 +856,17 @@ Noddy_traverse(Noddy *self, visitproc visit, void *arg)
}
\end{verbatim}
\note{Note that the \member{tp_traverse} implementation must name its
arguments exactly \var{visit} and \var{arg} in order to use
\cfunction{Py_VISIT()}. This is to encourage uniformity
across these boring implementations.}
We also need to provide a method for clearing any subobjects that can
participate in cycles. We implement the method and reimplement the
deallocator to use it:
\begin{verbatim}
static int
static int
Noddy_clear(Noddy *self)
{
PyObject *tmp;
@ -903,7 +908,7 @@ the careful decrementing of reference counts. With
simplified:
\begin{verbatim}
static int
static int
Noddy_clear(Noddy *self)
{
Py_CLEAR(self->first);
@ -973,7 +978,7 @@ later.
Here you can put a string (or its address) that you want returned when
the Python script references \code{obj.__doc__} to retrieve the
doc string.
Now we come to the basic type methods---the ones most extension types
will implement.
@ -1281,7 +1286,7 @@ to retrieve the descriptor from the class object, and get the
doc string using its \member{__doc__} attribute.
As with the \member{tp_methods} table, a sentinel entry with a
\member{name} value of \NULL{} is required.
\member{name} value of \NULL{} is required.
% XXX Descriptors need to be explained in more detail somewhere, but
@ -1345,7 +1350,7 @@ instance would be called. When an attribute should be deleted, the
third parameter will be \NULL. Here is an example that simply raises
an exception; if this were really all you wanted, the
\member{tp_setattr} handler should be set to \NULL.
\begin{verbatim}
static int
newdatatype_setattr(newdatatypeobject *obj, char *name, PyObject *v)
@ -1389,7 +1394,7 @@ static int
newdatatype_compare(newdatatypeobject * obj1, newdatatypeobject * obj2)
{
long result;
if (obj1->obj_UnderlyingDatatypePtr->size <
obj2->obj_UnderlyingDatatypePtr->size) {
result = -1;
@ -1489,7 +1494,7 @@ This function takes three arguments:
this is non-\NULL, raise a \exception{TypeError} with a message
saying that keyword arguments are not supported.
\end{enumerate}
Here is a desultory example of the implementation of the call function.
\begin{verbatim}

6
Include/objimpl.h
View file

@ -302,7 +302,11 @@ PyAPI_FUNC(void) PyObject_GC_Del(void *);
( (type *) _PyObject_GC_NewVar((typeobj), (n)) )
/* Utility macro to help write tp_traverse functions */
/* Utility macro to help write tp_traverse functions.
* To use this macro, the tp_traverse function must name its arguments
* "visit" and "arg". This is intended to keep tp_traverse functions
* looking as much alike as possible.
*/
#define Py_VISIT(op) \
do { \
if (op) { \